Poly(ethylene terephthalate), commonly referred to as PET, is used to make beverage bottles as well as other containers for household products. PET has become one of the most recycled plastics. During the recycle process, labels are typically separated from containers after the containers are ground into pieces. The label pieces are first loosed and detached from container pieces by being blown away in an air stream. Some of the label pieces are separated when caught up in the air stream. The remaining label pieces are separated from the container pieces by water flotation. The container pieces are recycled while the label pieces are typically discarded.
The density differences between water, labels and containers is utilized in the water floatation step. For example, PET flakes, which are heavier than water, will sink while the label materials, which are lighter than water, will float. Typical label materials that float and are best suitable for the recycle process include polyolefins and foamed polystyrene. Non-foamed polystyrene have been used, however their density is slightly higher than water. Thus, the density of water must be raised by the addition of salt, soaps or surfactants to accomodate the higher density of non-foamed polystyrene.
Polyesters have not been widely used to make labels because polyester labels are not readily separable from the containers. The density of polyesters is greater than that of water, thus the polyester labels would sink along with the container material. The density difference is significant enough that raising the density of water by additives is not economically viable. The option of recycling the polyester labels and bottles together has been considered. However, this is also not viable since the ink on the labels would cause contamination of the recycled polyesters.